Fig. 17 Severe pulmonary arterial hypertension in a 31- year-old man with a secundum ASD (subcostal view). + + margins of the secundum ASD (27 mm in diameter). RV: eccentric hypertrophy of the right ventricle.
Atrial septal defect
Atrial septal defect (ASD) is an abnormal opening in the atrial septum that allows for blood flow between the atria.
Types of ASD: ASD are most frequently diagnosed during adulthood and are more frequent in women than in men. Types of ASD are as follows:
* Secundum ASD: located at the level of the oval fossa; it is called secundum ASD despite the fact that the oval fossa is the septum primum (Fig. 17). Secundum ASD is the most common type of ASD and can exceed the true borders of the oval fossa.
* Primum ASD: primum ASD is part of the spectrum of AVSD. It is caused by a deficiency in the development of the AV septum during embryogenesis of the endocardial cushion. It is located anterior and inferior to the oval fossa, such that there is no atrial septal tissue between the lower edge of the defect and the AV valves, which are located on the same plane. It is bounded superiorly by the inferior border of the oval fossa and inferiorly by the superior and inferior bridging leaflet. Additional malformations are described in Atrioventricular Septal Defect (AVSD).
* Sinus venosus defect: this defect is caused by a deficiency of infolding of the atrial wall in the region of the embryogenic sinus venosus. There are two types of sinus venosus defects:
- The superior sinus venosus defect includes an interatrial communication located posterosuperior to the oval fossa and within the mouth of the superior vena cava, with the defect protruding over the rim of the oval fossa. Partial anomalous pulmonary venous connection to the superior vena cava is common (most often anomalous return of the right upper pulmonary vein). Total anomalous pulmonary venous connection of the right-sided pulmonary veins is rare.
- The inferior sinus venosus defect is located postero-inferiorly at the mouth of the inferior vena cava (it is very rare).
* Coronary sinus defect: there is an interatrial communication between the coronary sinus and the left atrium through the mouth of the coronary sinus (very rare). In its most extreme form, a left superior vena cava connects directly to the left atrium due to deficiency in the entire wall of the coronary sinus.
An ASD may be associated with a valvular pulmonary stenosis, mitral valvular prolapse, or Ebstein anomaly.
EPIDEMIOLOGY & DEMOGRAPHICS
• 80% of cases of ASD involve persistence of ostium secundum.
• Incidence is higher in females.
• ASD accounts for 8% to 10% of congenital heart abnormalities.
PHYSICAL FINDINGS & CLINICAL PRESENTATION
• Pansystolic murmur best heard at apex secondary to mitral regurgitation (ostium primum defect)
• Widely split S2
• Visible and palpable pulmonary artery pulsations
• Ejection systolic flow murmur
• Prominent right ventricular impulse
• Cyanosis and clubbing (severe cases)
• Exertional dyspnea
• Patients with small defects: generally asymptomatic
Clinical Features. Patients with a small left-to-right shunt, without volume overload, and without dilatation of the right ventricle do not complain of any symptoms. The diagnosis of an ASD is established, by chance, during the evaluation of a heart murmur or other disease.
Patients with a large left-to-right shunt and subsequent dilatation of both the right atrium and the right ventricle can complain of fatigue and dyspnea on exertion.
When severe pulmonary arterial hypertension has developed (which is rare, but facilitated in genetic predisposition), the shunt becomes bidirectional or reversed; the patients are symptomatic and cyanotic.
Early cyanosis is present in patients with a coronary sinus defect because systemic venous blood enters directly into the left atrium.
Precordial lift reflects right ventricular volume and pressure overload.
Pathophysiology. Volume overload of the right atrium and right ventricle due to a large left-to-right shunt is determined by the size of the interatrial communication. Pulmonary arterial hypertension and diastolic dysfunction with increased right ventricular filling pressures may develop in the presence of a hemodynamically relevant shunt during adulthood (usually in the fifth or sixth decade of life). The degree of left-to-right shunt decreases with age and may be bidirectional.
Severe pulmonary vascular disease with markedly increased pulmonary vascular resistance cannot be caused nor explained by an interatrial communication alone. A genetic predisposition to develop pulmonary vascular disease is present in patients with severely increased pulmonary vascular resistance; the pulmonary vascular bed is hyperreactive (see Fig. 17). The high pulmonary blood flow in the presence of a shunt acts as a trigger to initiate pathologic changes in the pulmonary vascular bed ending in the development of plexiform lesions. An interatrial shunt is never the only cause for pulmonary vascular disease. Patients with Down syndrome or TGA have a genetic predisposition to develop pulmonary vascular disease.
• Primary pulmonary hypertension
• Pulmonary stenosis
• Rheumatic heart disease
• Mitral valve prolapse
• Cor pulmonale
• Chest x-ray examination
• Cardiac catheterization
• ECG - A partial right bundle branch block is frequently present (a complete right bundle branch block is rare). An ectopic atrial rhythm is frequently associated with the presence of a superior sinus venosus defect. If severe pulmonary arterial hypertension is established, a right atrial P wave (P pulmonale) and right ventricular overload are recorded. QRS left-axis deviation reflects the presence of a primum ASD or AVSD.
1. Ostium primum defect: left axis deviation, RBBB, prolongation of PR interval
2. Sinus venous defect: leftward deviation of P axis
3. Ostium secundum defect: right axis deviation, right bundle-branch block
• Chest x-ray: cardiomegaly, enlargement of right atrium and ventricle, increased pulmonary vascularity, small aortic knob
• Echocardiography with saline bubble contrast and Doppler flow studies: may demonstrate the defect and the presence of shunting. Transesophageal echocardiography is much more sensitive than transthoracic echocardiography in identifying sinus venous defects and is preferred by some for the initial diagnostic evaluation.
• Cardiac catheterization: confirms the diagnosis in patients who are candidates for surgery. It is useful if the patient has some anatomic finding on echocardiography that is not completely clear or has significant elevation of pulmonary artery pressures.
Avoidance of strenuous activity in symptomatic patients
• Children and infants: closure of ASD before age 10 yr is indicated if pulmonary:systemic flow ratio is >1.5:1.
• Adults: closure is indicated in symptomatic patients with shunts >2:1.
• Surgery should be avoided in patients with pulmonary hypertension with reversed shunting (Eisenmenger’s syndrome) because of increased risk of right heart failure.
• Transcatheter closure is advocated in children when feasible.
• Prophylactic b-blocker therapy to prevent atrial arrhythmias should be considered in adults with ASD.
• Surgical closure is indicated in all patients with ostium primum defect and significant shunting unless patient has significant pulmonary vascular disease.
• Mortality is high in patients with significant ostium primum defect.
• Patients with small shunts have a normal life expectancy.
• Surgical mortality varies with the age of the patient and the presence of cardiac failure and systolic pulmonary artery hypertension; mortality ranges from <1% in young patients (<45 yr old) to >10% in elderly patients with presence of heart failure and systolic pulmonary hypertension.
• Preoperative atrial fibrillation is a risk factor for immediate postoperative and long-term atrial fibrillation.
• Thromboembolism after surgical repair of an ASD in an adult can occur in the early postoperative period. Giving early postoperative anticoagulation in patients >35 yr of age at the time of ASD repair and continuing it for at least 6 months will decrease the risk.